WASHINGTON — President Barack Obama called on Monday for a one-year extension of Bush-era tax cuts for families earning less than $250,000 a year, seeking to put Republicans on the defensive and reinforce his campaign mantra of being a middle-class champion.

Obama’s proposal is unlikely to sway his opponents in Congress, who have argued consistently that the Bush tax cuts should be extended for everyone, including higher earners.

“Let’s not hold the vast majority of Americans and our entire economy hostage while we debate the merits of another tax cut for the wealthy,” Obama said at the White House, standing in front of a riser filled with people who he said would be hurt if their tax cuts were not extended.

Republicans charge that allowing taxes to rise for wealthier Americans would hurt small business owners who are helping to create jobs in a tough economy, but Obama tried to neutralize that argument by saying 97 percent of all U.S. small business owners would fall under the $250,000-a-year income threshold.